Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide a method and an apparatus for video coding. In some embodiments, the apparatus includes processing circuitry. The processing circuitry can decode encoding information for a block of a picture in a coded video bitstream. The encoding information indicates a position of a sub-region in the block and a position of an additional sub-region in each of at least one neighboring block of the block. A combined sub-region includes the sub-region and the additional sub-region in each of the at least one neighboring block. The combined sub-region is at a center of a combined block including the block and the at least one neighboring block. The processing circuitry can reconstruct first samples that are inside the combined sub-region using residue data of the first samples and reconstruct second samples that are outside of the combined sub-region in the combined block without residue data.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation Application of U.S.application Ser. No. 16/218,233, filed Dec. 12, 2018, which claims thebenefit of priority to U.S. Provisional Application No. 62/696,530,filed on Jul. 11, 2018, the contents of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide a method and an apparatus for videocoding. In some embodiments, the apparatus includes processingcircuitry. The processing circuitry can decode encoding information fora block of a picture in a coded video bitstream. The encodinginformation indicates a position of a sub-region in the block and aposition of an additional sub-region in each of at least one neighboringblock of the block. A combined sub-region includes the sub-region andthe additional sub-region in each of the at least one neighboring block.The combined sub-region is at a center of a combined block including theblock and the at least one neighboring block. The processing circuitrycan reconstruct first samples that are inside the combined sub-regionusing residue data of the first samples and reconstruct second samplesthat are outside of the combined sub-region in the combined blockwithout residue data.

In an embodiment, the combined sub-region and the combined block have arectangular shape. In an example, a number of the at least oneneighboring block is one and the at least one neighboring block islocated to one of: the right of the block and below the block. In anexample, a number of the at least one neighboring block is three and theblock is located at a top-left corner of the combined block. In anexample, a width ratio of a width of the combined sub-region over awidth of the combined block is 1/2, and a height ratio of a height ofthe combined sub-region over a height of the combined block is 1/2.

In an embodiment, the block and the at least one neighboring block arecoded using inter prediction, and motion prediction information for theblock is different from motion prediction information for the at leastone neighboring block.

In an embodiment, the block and the at least one neighboring block arecoded using inter prediction, motion prediction information for theblock and the at least one neighboring block is signaled beforeinformation of the residue data of the first samples.

In an embodiment, the encoding information further indicates a size ofthe sub-region and a size of the additional sub-region in each of the atleast one neighboring block of the block.

Aspects of the disclosure provide a method for video coding. The methodcan include decoding encoding information for a block of a picture in acoded video bitstream where the encoding information indicates acombination of a position of a sub-region in the block and a relativesize of the sub-region with respect to the block. First samples insidethe sub-region are reconstructed using residue data of the firstsamples, second samples of the block that are outside of the sub-regionare reconstructed without residue data, and the combination of theposition and the relative size is one of multiple combinations ofdifferent positions and different relative sizes. The method includesreconstructing the first samples of the block that are inside thesub-region using the residue data of the first samples andreconstructing the second samples of the block that are outside of thesub-region without residue data.

In an embodiment, the block and the sub-region have a rectangular shape.The relative size is associated with a width ratio being a width of thesub-region over a width of the block and a height ratio being a heightof the sub-region over a height of the block. The multiple combinationsof different positions and different relative sizes include: 1) theposition is a center of the block, the width ratio and the height ratioare 1/2, 2) the position is a center of the block, the width ratio is1/2 and the height ratio is 1, 3) the position is a left side of theblock, the width ratio is 1/4 and the height ratio is 1, 4) the positionis a right side of the block, the width ratio is 1/4 and the heightratio is 1, 5) the position is a center of the block, the width ratio is1 and the height ratio is 1/2, 6) the position is a top side of theblock, the width ratio is 1 and the height ratio is 1/4, and 7) theposition is a bottom side of the block, the width ratio is 1 and theheight ratio is 1/4.

In an embodiment, the encoding information includes an index indicatingthe one of the multiple combinations of different positions anddifferent relative sizes. The method further includes receiving theindex in the coded video bitstream. In an embodiment, the differentrelative sizes include a relative size of the sub-region being 1/4 ofthe block.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows Givens rotations according to an embodiment.

FIG. 9 shows a flowchart of a Hypercube-Givens Transform (HyGT) for a 16elements NSST according to an embodiment.

FIG. 10 shows HyGT rounds and an optional permutation pass according toan embodiment.

FIG. 11 shows examples of spatially varying transform (SVT) patternsaccording to some embodiments.

FIG. 12 shows examples of SVT patterns according to some embodiments.

FIG. 13 shows examples of SVT patterns according to some embodiments.

FIG. 14 shows examples of SVT patterns associated with combinedsub-regions according to some embodiments.

FIG. 15 shows a flow chart outlining a process according to anembodiment.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(2 00) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example mega samples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any color space (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

A picture can be split into a plurality of CTUs. In some examples, a CTUis split into CUs by using a quadtree (QT) structure denoted as a codingtree to adapt to various local characteristics of the picture. Thedecision whether to code a picture area using an inter-pictureprediction (also referred to as a temporal prediction or an interprediction type), an intra-picture prediction (also referred to as aspatial prediction, or an intra-prediction type), and the like is madeat the CU level. In an embodiment, each CU can be further split intoone, two or four PUs according to a PU splitting type. Inside one PU,the same prediction process is applied and the same predictioninformation is transmitted to a decoder on a PU basis. After obtainingresidual data or residual information by applying the prediction processbased on the PU splitting type, the CU can be partitioned into TUsaccording to another QT structure similar to the coding tree for the CU.In an example, a transform is applied for each TU, and a TU has the sametransform information. The HEVC structure has multiple partition unitsincluding a CU, a PU, and a TU. Samples in a CU can have the sameprediction type, samples in a PU can have the same predictioninformation, and samples in a TU can have same transform information. ACU or a TU is limited to a square shape, while a PU can have a square ora rectangular shape for an inter-predicted block according to anembodiment. Further, PUs having rectangular shapes can be used for anintra prediction in an embodiment. In an embodiment, such as in the VVCstandard, each CU only contains one PU, and the CU (or PU) and a TU canhave a rectangular shape.

An implicit QT split is applied to a CTU located at a picture boundaryto recursively split the CTU into a plurality of CUs so that each CU islocated inside the picture boundary.

In general, an inter prediction, an intra-prediction, and/or the likecan be used for prediction in some embodiments. The intra-prediction canhave 67 intra prediction modes (or intra modes) including a DC mode, aplanar mode, and 65 angular modes (also referred to as directional intraprediction modes or directional intra modes) corresponding to 65 angulardirections, respectively. To accommodate the 65 directional intra modes,an intra mode coding method with 6 Most Probable Modes (MPMs) can beused. The intra mode coding method can include derivation of the 6 MPMsand entropy coding of the 6 MPMs and 61 non-MPM modes.

A MPM list can include modes in the 6 MPMs. The modes in the MPM listcan be classified into three groups: a first group including neighboringintra prediction modes (also referred to as neighbor intra modes), asecond group including derived intra modes, and a third group includingdefault intra modes. In an example, five neighboring intra predictionmodes from the first group are used to form a MPM list. When the MPMlist is not full (i.e., there are less than 6 MPM candidates in the MPMlist), one or more derived intra modes from the second group are added.The one or more derived intra modes can be obtained by adding −1 or +1to one or more angular modes in the MPM list. In an example, the one ormore derived modes are not generated from non-angular modes includingthe DC mode and the planar mode. Further, when the MPM list is still notfull, one or more default intra modes from the third group are added ina following order: the vertical intra mode, the horizontal intra mode,the intra mode 2, and the diagonal intra mode. Accordingly, the MPM listof the 6 MPM modes is generated.

The 61 non-MPM modes can be coded as follows. The 61 non-MPM modes canbe divided into two sets: a selected mode set (referred to as secondaryMPMs) and a non-selected mode set. The selected mode set includes 16 ofthe 61 non-MPM modes and the non-selected mode set includes 45 of theremaining of the 61 non-MPM modes. In an example, a flag in a bitstreamcan be used to indicate a mode set (i.e., the selected mode set or thenon-selected mode set) to which the current intra mode belongs. When thecurrent intra mode is in the selected mode set, the current mode issignaled with a 4-bit fixed-length code, and when the current intra modeis in the non-selected mode set, the current intra mode is signaled witha truncated binary code.

In general, residual coding is implemented for both inter and intracoded blocks. For example, a prediction error or residue of a blockafter prediction can be transformed into transform coefficients andsubsequently coded. In an example, such as in the HEVC standard,discrete cosine transform (DCT) kernel of type II (DCT-II) and 4×4discrete sine transform (DST) kernel of type VII (DST-VII) can beemployed for transform, such as in a forward core transform at anencoder side and an inverse core transform at a decoder side. Inaddition to DCT-II and 4×4 DST-VII, an Adaptive Multiple core Transform(AMT) or Enhanced Multiple Transform (EMT) method is used for residualcoding for both inter and intra coded blocks. In the AMT, multipleselected transforms from the DCT/DST families other than, for example,the current transforms in the HEVC standard, can be used. The multipleselected transforms from the DCT/DST families can include DST-VII,DCT-VIII, DST-I, DCT-V, and the like. Table 1 shows basis functions ofcertain DST/DCT transforms.

In order to maintain orthogonality of a transform matrix, the transformmatrix can be quantized more accurately with a 10-bit representationinstead of an 8-bit representation. To keep intermediate values oftransformed coefficients within a range of 16-bits, after a horizontaland/or after a vertical transform, the transformed coefficients areright shifted by 2 more bits, for example, comparing to the 7 bit rightshift after the first vertical inverse transform used in the HEVCtransforms.

In an example, an AMT is applicable to CUs with both a width and aheight that is smaller than or equal to 64, and whether an AMT isapplicable can be controlled by a CU level flag. When the CU level flagis 0, a DCT-II is applied in the CU to encode a residue of the CU. For aluma coding block within an AMT enabled CU, two additional flags aresignaled to identify the respective horizontal and vertical transform tobe used. The residue of the block can be coded with a transform skipmode. To avoid redundancy of syntax coding, the transform skip flag isnot signaled when the CU level flag is not zero.

TABLE 1 Transform basis functions of DCT-II/V/VIII and DST-I/VII for anN-point input. Transform Type Basis function T_(i)(j), i, j = 0, 1, . .. , N − 1 DCT-II${T_{i}(j)} = {\omega_{0} \cdot \sqrt{\frac{2}{N}} \cdot \left( \frac{\pi \cdot i \cdot \left( {{2j} + 1} \right)}{2N} \right)}$${{where}\mspace{14mu} \omega_{0}} = \left\{ \begin{matrix}\sqrt{\frac{2}{N}} & {i = 0} \\1 & {i \neq 0}\end{matrix} \right.$ DCT-V${{T_{i}(j)} = {\omega_{0} \cdot \omega_{1} \cdot \sqrt{\frac{2}{{2N} - 1}} \cdot {\cos \left( \frac{2{\pi \cdot i \cdot j}}{{2N} - 1} \right)}}},$${{where}\mspace{14mu} \omega_{0}} = \left\{ {\begin{matrix}\sqrt{\frac{2}{N}} & {i = 0} \\1 & {i \neq 0}\end{matrix},{\omega_{1} = \left\{ \begin{matrix}\sqrt{\frac{2}{N}} & {j = 0} \\1 & {j \neq 0}\end{matrix} \right.}} \right.$ DCT-VIII${T_{i}(j)} = {\sqrt{\frac{4}{{2N} + 1}} \cdot {\cos \left( \frac{\pi \cdot \left( {{2i} + 1} \right) \cdot \left( {{2j} + 1} \right)}{{4N} + 2} \right)}}$DST-I${T_{i}(j)} = {\sqrt{\frac{2}{N + 1}} \cdot {\sin \left( \frac{\pi \cdot \left( {i + 1} \right) \cdot \left( {j + 1} \right)}{N + 1} \right)}}$DST-VII${T_{i}(j)} = {\sqrt{\frac{4}{{2N} + 1}} \cdot {\sin \left( \frac{\pi \cdot \left( {{2i} + 1} \right) \cdot \left( {j + 1} \right)}{{2N} + 1} \right)}}$

In an embodiment, for an intra residue coding, due to different residuestatistics associated with different intra prediction modes, amode-dependent transform candidate selection process can be used. Threetransform subsets can be defined as shown in Table 2, and a transformsubset is selected based on an intra prediction mode, as specified inTable 3. For example, a transform subset is identified based on Table 3using an intra prediction mode of a CU when the CU level flag is 1 whichindicates that AMT is used. In addition, for each of the horizontal andthe vertical transforms, one of two transform candidates in theidentified transform subset is selected based on explicit signallingwith one or more flags and Table 2.

TABLE 2 Three pre-defined transform candidate sets Transform SetTransform Candidates 0 DST-VII, DCT-VIII 1 DST-VII, DST-I 2 DST-VII,DCT-VIII

TABLE 3 Examples of horizontal and vertical transform sets for eachintra prediction mode Intra Mode 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 V 2 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 0 H 2 1 0 1 0 1 0 1 0 1 0 1 01 2 2 2 2 Intra Mode 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34V 0 0 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 H 2 2 2 2 2 1 0 1 0 1 0 1 0 1 0 1 0Intra Mode 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 V 1 0 10 1 0 1 0 1 0 1 2 2 2 2 2 2 2 H 1 0 1 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0Intra Mode 53 54 55 56 57 58 59 60 61 62 63 64 65 66 V 2 2 1 0 1 0 1 0 10 1 0 1 0 H 0 0 1 0 1 0 1 0 1 0 1 0 1 0

In an embodiment, for an inter residue coding, one transform setincluding DST-VII and DCT-VIII can be used for various inter predictionmodes and for both the horizontal and the vertical transforms.

Complexity of an AMT can be relatively high at an encoder side, forexample, when a brute-force search is used where five (DCT-II and fourmultiple transform candidates as shown in Table 1) different transformcandidates are evaluated with a rate-distortion cost for each residualblock. To alleviate the complexity of the AMT at the encoder side,various optimization methods can be designed for algorithm acceleration,for example, in the JEM standard.

In an embodiment, a mode-dependent non-separable secondary transform(NSST) can be used between a forward core transform and a quantizationat an encoder side and between a de-quantization and an inverse coretransform at a decoder side. For example, to keep a low complexity, aNSST is applied to low frequency coefficients after a primary transform(or a core transform). When both a width (W) and a height (H) of atransform coefficient block are larger than or equal to 8, an 8×8 NSSTis applied to a top-left 8×8 region of the transform coefficients block.Otherwise, when either the width W or the height H of the transformcoefficient block is 4, a 4×4 NSST is applied, and the 4×4 NSST isperformed on a top-left min(8,W)×min(8,H) region of the transformcoefficient block. The above transform selection method is applied forboth luma and chroma components.

A matrix multiplication implementation of a NSST is described as followsusing a 4×4 input block as an example. The 4×4 input block X is writtenin Eq. (1) as

$\begin{matrix}{X = \begin{bmatrix}X_{00} & X_{01} & X_{02} & X_{03} \\X_{10} & X_{11} & X_{12} & X_{13} \\X_{20} & X_{21} & X_{22} & X_{23} \\X_{30} & X_{31} & X_{32} & X_{33}\end{bmatrix}} & (1)\end{matrix}$

The input block X can be represented as a vector

in Eq. (2) where

{right arrow over (X)}=[X ₀₀ X ₀₁ X ₀₂ X ₀₃ X ₁₀ X ₁₁ X ₁₂ X ₁₃ X ₂₀ X₂₁ X ₂₂ X ₂₃ X ₃₀ X ₃₁ X ₃₂ X ₃₃]^(T)  (2)

The non-separable transform is calculated as

=T·

where

indicates a transform coefficient vector, and T is a 16×16 transformmatrix. The 16×1 transform coefficient vector

is subsequently reorganized as a 4×4 block using a scanning order (forexample, a horizontal scanning order, a vertical scanning order or adiagonal scanning order) for the input block X. Coefficients withsmaller indices can be placed with smaller scanning indices in the 4×4coefficient block. In some embodiments, a Hypercube-Givens Transform(HyGT) with a butterfly implementation can be used instead of the matrixmultiplication described above to reduce the complexity of the NSST.

In an example, 35×3 non-separable secondary transforms are available forboth 4×4 and 8×8 block sizes, where 35 is a number of transform setsassociated with the intra prediction modes, and 3 is a number of NSSTcandidates for each intra prediction mode. Table 4 shows an exemplarymapping from an intra prediction mode to a respective transform set. Atransform set applied to luma/chroma transform coefficients is specifiedby a corresponding luma/chroma intra prediction mode, according to Table4. For an intra prediction mode larger than 34, which corresponds to adiagonal prediction direction, a transform coefficient block istransposed before/after the NSST at the encoder/decoder, respectively.

For each transform set, a selected NSST candidate can be furtherspecified by an explicitly signaled CU level NSST index. The CU levelNSST index is signaled in a bitstream for each intra coded CU aftertransform coefficients and a truncated unary binarization is used forthe CU level NSST index. For example, a truncated value is 2 for theplanar or the DC mode, and 3 for an angular intra prediction mode. In anexample, the CU level NSST index is signaled only when there is morethan one non-zero coefficient in the CU. The default value is zero andnot signaled, indicating that a NSST is not applied to the CU. Each ofvalues 1-3 indicates which NSST candidate is to be applied from thetransform set.

TABLE 4 Mapping from an intra prediction mode to a transform set indexIntra mode 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 set 0 1 2 3 4 5 6 78 9 10 11 12 13 14 15 16 Intra mode 17 18 19 20 21 22 23 24 25 26 27 2829 30 31 32 33 set 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33Intra mode 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 set 34 3332 31 30 29 28 27 26 25 24 23 22 21 20 19 18 Intra mode 51 52 53 54 5556 57 58 59 60 61 62 63 64 65 66 67 (LM) set 17 16 15 14 13 12 11 10 9 87 6 5 4 3 2 NULL

In some embodiments, a NSST is not applied for a block coded with atransform skip mode. When the CU level NSST index is signaled for a CUand not equal to zero, a NSST is not used for a block that is coded withthe transform skip mode in the CU. When the CU with blocks of allcomponents are coded in a transform skip mode or a number of non-zerocoefficients of non-transform-skip mode CBs is less than 2, the CU levelNSST index is not signaled for the CU.

In an example, a NSST and an EMT are not used for a same CU when a QTBTis used for partition, and thus a NSST is used when DCT2 is used as aprimary transform.

A HyGT is used in the computation of a NSST. Basic elements of theorthogonal HyGT are Givens rotations that are defined by orthogonalmatrices G(m, n, θ) as follows:

$\begin{matrix}{{G_{i,j}\left( {m,n} \right)} = \left\{ {\begin{matrix}{{\cos \mspace{11mu} \theta},} & {{i = {j = {{m\mspace{14mu} {or}\mspace{14mu} i} = {j = n}}}},} \\{{\sin \mspace{11mu} \theta},} & {{i = m},{j = n},} \\{{{- \sin}\mspace{11mu} \theta},} & {{i = n},{j = m},} \\{1,} & {{i = {{j\mspace{14mu} {and}\mspace{14mu} i} \neq {m\mspace{14mu} {and}\mspace{14mu} i} \neq n}},} \\{0,} & {otherwise}\end{matrix}.} \right.} & (2)\end{matrix}$

FIG. 8 shows Givens rotations according to an embodiment of thedisclosure. In an embodiment, the HyGT is implemented by combining setsof Givens rotations in a hypercube arrangement. FIG. 9 shows a“butterfly” shape flowchart (910) of the HyGT for a 16 elements (i.e.,4×4) NSST according to an embodiment of the disclosure. In an example, aHyGT round is defined as a sequence of log 2(N) passes where N is apower of two. In each pass, the indices in vectors m and n are definedby edges of a hypercube with a dimension of log 2(N), sequentially ineach direction.

To obtain good compression, more than one HyGT round can be used. Asshown in FIG. 10, a full NSST (1010) can include R HyGT rounds (R is apositive integer) and an optional permutation pass (1020) to sorttransform coefficients according to corresponding variance. For example,in the JEM standard, 2 HyGT rounds are applied for a 4×4 NSST and 4 HyGTrounds are applied for an 8×8 NSST.

In some embodiments, samples in a CU are predicted using interprediction to generate residual data of the samples. Subsequently,transform coefficients can be determined by applying a transform on theresidual data of the samples in the CU. Alternatively, a CU can includea sub-region (also referred to as a first sub-region) and a remainingsub-region that is outside the sub-region (also referred to as a secondsub-region). Transform coefficients of samples in the first sub-region(referred to as first samples) can be determined by applying a transformon residual data of the first samples in the first sub-region and notransform is performed on samples in the second sub-region (referred toas second samples. Therefore, the transform is applied to a portion(i.e., the first sub-region) of the CU that is less than the CU, andthus, the transform is referred to as a spatially varying transform(SVT). In some embodiments, residual data of the second sub-region arerelatively small and can be forced to be zero.

In some examples, when a root level coded block flag indicates that thesamples in the CU have non-zero transform coefficients (for example,root_cbf=1), a SVT flag (i.e, a svt_flag) can be signaled to indicatewhether a SVT is used. In an example, when the SVT flag is 0, the SVT isnot used, and a transform is applied to the samples of the CU. When theSVT flag is 1, the SVT is used, and a transform is applied to the firstsamples in the first sub-region of the CU. The first sub-region can bereferred to as a TU.

In some embodiments, when a SVT is used for a CU, a SVT type and/or SVTposition information can be encoded in a coded video bitstream at anencoder side and decoded from the coded video bitstream at a decoderside. Further, a specific SVT pattern, i.e., a specific arrangement of aTU within the CU, such as a width ratio of a TU width over a CU width, aheight ratio of a TU height over a CU height, a position of the TU withrespect to the CU, and the like, can be determined based on the SVT typeand/or the SVT position information.

FIG. 11 shows SVT patterns of two SVT types, each with three SVTpositions, according to an embodiment of the disclosure. The two SVTtypes include a vertical SVT (SVT-V) and a horizontal SVT (SVT-H). ThreeSVT patterns (1101), (1111), and (1121) with different SVT positionscorrespond to the SVT-V in which the TU width equals to 1/2 of the CUwidth W (i.e., the width ratio is 1/2) and the TU height is equal to theCU height H (i.e., the height ratio is 1). Further, the three TUpositions are positioned at i/4 of the CU width W from a top-left cornerof the respective CU (1103), (1113), and (1123), where i is 0, 1 and 3,respectively. The three positions are denoted as a vertical position 0,1 and 2, respectively. TUs (1102), (1112), and (1122) are associatedwith the respective CUs (1103), (1113), and (1123), respectively.

Similarly, three SVT patterns (1131), (1141), and (1151) with differentSVT positions correspond to the SVT-H in which the TU height equals to1/2 of the CU height H (i.e., the height ratio is 1/2), the TU width isequal to the CU width W (i.e., the width ratio is 1), and the three TUpositions are positioned at i/4 of the CU height H from a top-leftcorner of the respective CU (1133), (1143), and (1153), where i is 0, 1and 3, respectively. The three positions are denoted as a horizontalposition 0, 1 and 2, respectively. TUs (1132), (1142), and (1152) areassociated with the respective CUs (1133), (1143), and (1153),respectively.

Both TU and CU boundaries can be filtered by de-blocking filtering. Inan embodiment, the SVT-V (or the SVT-H) is enabled when a CU width (or aCU height) is in a range of [8, 32]. To ensure that a gap between twofiltered boundaries is larger than or equal to 4 pixels, for example,the vertical position 1 is disabled when the CU width is smaller than orequal to 8 pixels, and the horizontal position 1 is disabled when the CUheight is smaller than or equals to 8 pixels,

A position-dependent core transform can be applied in the SVT where thethree horizontal and vertical positions are associated with differentcore transforms. Table 5 shows an example of the horizontal and verticaltransforms for the SVT patterns described above.

To reduce complexity of the SVT, the SVT is applied to certain modesaccording to some embodiments. For example, the SVT is applied to amerge mode (for the first two merge candidates) and an advanced motionvector prediction (AMVP) mode, but not to inter prediction modesincluding affine mode, a frame rate up conversion (FRUC) and integermotion vector resolution (IMV) in Benchmark Set (BMS) 1.0.

A fast algorithm can be designed for the SVT according to someembodiments. For each SVT pattern (or SVT mode), a rate distortion (RD)cost is estimated based on a sum of square differences (SSD) of aresidual-skipped part. An SVT mode is skipped in a rate distortionoptimization (RDO) when the estimated RD cost of the SVT mode is largerthan an actual RD cost of the best mode. In addition, only the bestthree SVT modes in terms of the estimated RD cost are tried in the RDO.

TABLE 5 Horizontal and vertical transforms for different SVT types andpositions horizontal vertical SVT type, position transform transformSVT-V, position 0 DCT-8 DST-7 SVT-V, position 1 DST-1 DST-7 SVT-V,position 2 DST-7 DST-7 SVT-H, position 0 DST-7 DCT-8 SVT-H, position 1DST-7 DST-1 SVT-H, position 2 DST-7 DST-7

In some embodiments, residual data of first samples in the firstsub-region are relatively large and are encoded and transmitted to adecoder. Residual data of second samples in the second sub-region arerelatively small and are not encoded. According to aspects of thedisclosure, in a SVT, the first samples of the CU that are inside thefirst sub-region are reconstructed using the residual data of the firstsamples while the second samples of the CU that are outside the firstsub-region are reconstructed without residual data. In general, thefirst sub-region can have any suitable shape and size, and can belocated at any suitable position inside the CU. A shape, a size, and/ora position of the first sub-region can depend on the residual data ofthe samples in the CU. As will be described below, according to aspectsof the disclosure, an area of the first sub-region is 1/4 of an area ofthe CU according to an embodiment. Further, the first sub-region can belocated at any suitable position inside the CU. For example, the firstsub-region can be at a center of the CU and separated from all edges ofthe CU.

As described above, the CU can be separated into different sub-regionsbased on the residual data (or the motion compensated residues) of thesamples. The CU includes the first sub-region (i.e., a large residuesub-region) having the first samples with the relatively large residuesand the second sub-region (i.e., a small residue sub-region) havingsecond samples with the relatively small residues. Various methods canbe used to determine the first sub-region and the second sub-region. Inan example, the first sub-region and the second sub-region can bedetermined based on the residual data of the samples. For example, theresidual data of the samples in the CU can be compared with apre-determined residue threshold. The residual data of the first samplesin the first sub-region are above the pre-determined residue thresholdwhile the residual data of the second samples in the second sub-regionare below or equal to the pre-determined residue threshold.Alternatively, the first sub-region and the second sub-region can bedetermined based on quantized transform coefficients associated with theresidual data of the samples. For example, the first samples in thefirst region have non-zero quantized transform coefficients, and thesecond samples in the second region have no non-zero quantized transformcoefficients.

At an encoder side, the transform coefficients of the first samples inthe first sub-region can be determined by applying a transform on theresidual data of the first samples inside the first sub-region. Further,the residual data of the second samples inside the second sub-region isnot encoded. In an example, the relatively small residual data of thesecond samples can be set to zero. Accordingly, at a decoder side, theresidual data of the first samples inside the first sub-region can bedetermined by implementing an inverse transform of the transformcoefficients of the first samples, for example, received from a codedvideo bitstream.

FIG. 12 shows SVT patterns (1201), (1211), (1221), and (1231) accordingto some embodiments of the disclosure. Referring to FIG. 12, each CU(1203), (1213), (1223), and (1233) and a respective first sub-region(1202), (1212), (1222), and (1232) have a rectangular shape. In the toprow, a width of each of the first sub-region (1202) and (1212) is 1/4 ofa width (W) of each of the CU (1203) and (1213), resulting in a widthratio of 1/4, and each of the CUs (1203) and (1213) can be splitvertically. A height of each of the first sub-region (1202) and (1212)is equal to a height (H) of each of the CUs (1203) and (1213). The firstsub-region (1202) is adjacent to a left edge (1204) of the CU (1203).The first sub-region (1212) is adjacent to a right edge (1214) of the CU(1213). In the bottom row, a width of each of the first sub-region(1222) and (1232) is equal to a width (W) of each of the CUs (1223) and(1233), and each of the CU (1223) and (1233) can be split horizontally.A height of each of the first sub-regions (1222) and (1232) is 1/4 of aheight (H) of each of the CUs (1223) and (1233), resulting in a heightratio of 1/4. The first sub-region (1222) is adjacent to a top edge(1224) of the CU (1223). The first sub-region (1232) is adjacent to abottom edge (1234) of the CU (1233).

Referring to FIGS. 11 and 12, the SVT patterns (1101) and (1201) aresimilar except that a width ratio of 1/4 of the SVT pattern (1201) issmaller than a width ratio of 1/2 of the SVT pattern (1101).Accordingly, when a size of the CU (1103) is identical to a size of theCU (1203), a transform implemented on first samples in the firstsub-region (1202) can be more efficient than a transform implemented onthe first samples in the first sub-region (1102) because a number of thefirst samples in the first sub-region (1202) is less than a number ofthe first samples in first sub-region (1102). Therefore, when samples inthe CU (1203) that have relatively large residues are located (orconcentrated), for example, in 1/4 of the area of the CU (1203) and arenear the left edge (1204), the SVT pattern (1201) is used instead of theSVT pattern (1101). A similar description is applicable to other SVTpatterns, such as the SVT patterns (1121) and (1211), the SVT patterns(1131) and (1221), and the SVT patterns (1151) and (1231).

In some embodiments, first samples in a CU that have relatively largeresidues can be located (or concentrated) near a center of the CU or ata corner of the CU. Accordingly, SVT patterns that are different fromthe SVT patterns shown in FIGS. 11-12 can be used. FIG. 13 shows SVTpatterns according to some embodiments of the disclosure. Each CU(1303), (1313), (1323), (1333), and (1343) and a respective firstsub-region (1302), (1312), (1322), (1332), and (1342) have a squareshape. Further, a width of each of the first sub-regions (1302), (1312),(1322), (1332), and (1342) is 1/4 of a width (W) of each of the CUs(1303), (1313), (1323), (1333), and (1343), respectively. Further, aheight of each of the first sub-regions (1302), (1312), (1322), (1332),and (1342) is 1/4 of a height (H) of each of the CUs (1303), (1313),(1323), (1333), and (1343), respectively. Thus, a width ratio and aheight ratio is 1/4. The first sub-region (1302) is at a center of theCU (1303), and is separated from all edges of the CU (1303). In anexample, the center of the CU (1303) can be determined implicitly, andthus, no position information is signaled for the SVT pattern (1301).The first sub-region (1312) is at a top-left corner of the CU (1313),the first sub-region (1322) is at a top-right corner of the CU (1323),the first sub-region (1332) is at a bottom-left corner of the CU (1333),and the first sub-region (1342) is at a bottom-right corner of the CU(1343). Accordingly, positions of the respective first sub-regions(1312), (1322), (1332), and (1342) are signaled.

In some examples, samples in a CU shown in FIGS. 12-13 are coded usinginter prediction, and first and second samples in the CU have the samemotion prediction information. For example, for the SVT pattern (1201)in the FIG. 12 example, the first samples in the first sub-region (1202)and the second samples in the CU that are outside the first sub-region(1202) can have the same motion prediction information.

A suitable SVT pattern can be selected from a group of SVT patterns, andthus, one or more indices to indicate characteristics of a firstsub-region in a CU such as a position and/or a size of the firstsub-region can be coded. In an example, context-adaptive binaryarithmetic coding (CABAC) with a variable-length binarization can beused to code the one or more indices. In an example, positioninformation can be signaled in the coded video bitstream, andsubsequently decoded by a decoder.

In general, the SVT patterns in the group can include any suitable SVTpatterns, such as one or more of the SVT patterns shown in FIGS. 11-13.In an example, a SVT group includes seven SVT patterns: (1111) and(1141) in FIG. 11, (1201), (1211), (1221), and (1231) in FIG. 12, and(1301) in FIG. 13. Table 6 shows an example of binarization associatedwith the SVT group according to an aspect of the disclosure. In anexample, a first bin and a second bin of bins in the binarization codeindicate whether a first sub-region is located at a center of the CU andwhether the CU is split horizontally or vertically. Referring to Table6, a ‘0’ in the first bin indicates that the first sub-region is locatedat the center position, thus coding the SVT pattern (1301) and having anindex of 0, a ‘10’ in the first bin and the second bin indicates thatthe CU is split vertically, and coding one of the SVT patterns (1111),(1201), and (1211). Further, an ‘11’ in the first bin and the second binindicates that the CU is split horizontally, and coding one of the SVTpatterns (1141), (1221), and (1231). The first and second bins can usedifferent contexts to code. Another context can be used for other bins.

FIGS. 11-13 illustrate a first sub-region in a SVT pattern of differentshapes, sizes, and positions within a respective CU. The size of thefirst sub-region can be represented using a width ratio and a heightratio. Alternatively, the size of the first sub-region can berepresented using an area ratio of an area of the first sub-region overan area of the CU. The area ratio can be 1/4, 1/2, or the like. Thewidth ratio and the height ratio can be 1/4, 1/2, 1, or the like. Theposition of the first sub-region can be at a center, at a corner, at anedge, or the like.

Table 6 shows an example of binarization associated with the SVT group

Index binarization SVT pattern 0 0 1301 1 101 1111 2 1000 1201 3 10011211 4 111 1141 5 1100 1221 6 1101 1231

As described above, a first sub-region is within a CU, and a singletransform is implemented for first samples in the first sub-region.However, in some embodiments, multiple first sub-regions in adjacentneighboring CUs include first samples that have relatively largeresidues. In this case, a combined sub-region can be formed thatincludes the multiple first sub-regions that extend beyond one or moreboundaries between the multiple CUs. Instead of implementing separatetransforms for the first samples in the respective first sub-regions, asingle transform is implemented for the first samples in the combinedsub-region according to aspects of the disclosure, and thus improvingcoding efficiency. In general, the multiple CUs and the respective firstsub-regions can have any suitable shapes, sizes, and relative positions,and thus, the combined sub-region and the combined CU can have anysuitable shapes, sizes, and relative positions. Further, a number of themultiple CUs is an integer larger than 1.

FIG. 14 shows SVT patterns associated with combined sub-regionsaccording to some embodiments of the disclosure. In the FIG. 14examples, the combined sub-region is at a center of a combined CUincluding the multiple CUs.

In some examples, first sub-regions in 2 CUs are combined. For example,a SVT pattern (1405) is shown where a combined CU (1401) includes a CU(1402) and a CU (1412). The CU (1412) is adjacent to and is located tothe right of the CU (1402). The CU (1402) includes a first sub-region(1403) having first samples with relatively large residues and a secondsub-region (1404) that is outside the first sub-region (1403) havingsecond samples with relatively small residues. Similarly, the CU (1412)includes a first sub-region (1413) having first samples and a secondsub-region (1414) that is outside the first sub-region (1413) havingsecond samples. A combined sub-region (1411) including the firstsub-regions (1403) and (1413) is located at a center of the combined CU(1401). In the FIG. 14 example, the CUs (1402) and (1412) share a sameboundary (1418), and the combined sub-region (1411) can override (orextend beyond) the boundary (1418). The combined sub-region (1411) islocated within the CU (1402) and the CU (1412).

In the FIG. 14 example, the combined sub-region (1411) and the combinedCU (1401) have a rectangular shape, a width ratio of a width of thecombined sub-region (1411) over a width of the combined CU (1401) isequal to a first ratio, and a height ratio of a height of the combinedsub-region (1411) over a height of the combined CU (1401) is equal to asecond ratio. In an example, the first ratio is different from thesecond ratio. In another example, such as shown in FIG. 14, the firstratio is equal to the second ratio, and is 1/2, and thus, an area of thecombined sub-region (1411) is 1/4 of the combined CU (1401).

At an encoder side, transform coefficients of the first samples in thecombined sub-region (1411) can be determined by applying a singletransform on the residual data of the first samples inside the combinedsub-region (1411). Further, the residual data of the second samples ofthe combined CU (1401) that are outside the combined sub-region (1411)are not encoded. For example, the residual data of the second samplesare not transformed into transform coefficients.

At a decoder side, the residual data of the first samples inside thecombined sub-region (1411) can be determined by implementing an inversetransform of the transform coefficients of the first samples, forexample, received from a coded video bitstream. Further, the firstsamples in the combined sub-region (1411) can be reconstructed using theresidual data of the first samples, and the second samples can bereconstructed without residue data. For example, the transformcoefficients of the second samples are not coded and are inferred to be0. The CUs (1402) and (1412) can be coded with different motionprediction information. Further, non-residue information including thedifferent motion prediction information of the CUs (1402) and (1412) issignaled before residue information associated with the CUs (1402) and(1412), and the residue information can include residual data associatedwith the combined sub-region (1411), information indicating a SVTpattern, a size, a shape, and a location of the combined sub-region(1411), and/or the like.

In the SVT pattern (1405), both the combined sub-region (1411) and thecombined CU (1401) have a rectangular (and non-square) shape. In anotherexample, a SVT pattern (1435) is shown where a combined CU (1431)includes a CU (1432) and a CU (1442) that is adjacent to the CU (1432).A combined sub-region (1441) and the combined CU (1431) have a squareshape, and the combined sub-region (1441) is located at a center of thecombined CU (1431). The CU (1432) includes a first sub-region (1433),and the CU (1442) includes a first sub-region (1443) that is adjacent tothe first sub-region (1433). Operations similar to those described abovecan be implemented for the combined sub-region (1441) and the combinedCU (1431) at an encoder and a decoder side, respectively, and thus, adetailed description is omitted for purposes of clarity.

In another example, a SVT pattern (1425) is shown where a combined CU(1421) includes a CU (1422) and a CU (1423), which is adjacent to the CU(1422). As illustrated in FIG. 14, the CU (1423) is above the CU (1422).A combined sub-region (1427) is located at a center of the combined CU(1421). The CU (1422) includes a first sub-region (1424), and the CU(1423) includes a first sub-region (1426) that is adjacent to and abovethe first sub-region (1424). Operations similar to those described abovecan be implemented for the combined sub-region (1427) and the combinedCU (1421) at an encoder and a decoder side, respectively, and thus, adetailed description is omitted for purposes of clarity.

In another example, a number of the multiple CUs is 4, as shown in a SVTpattern (1459). A combined CU (1455) includes 4 neighboring CUs(1451)-(1454). The CUs (1451)-(1454) include neighboring firstsub-regions (1461-1464), respectively. In an example, the firstsub-region (1461) is at a bottom-right corner of the CU (1451), thefirst sub-region (1462) is at a bottom-left corner of the CU (1452), thefirst sub-region (1463) is at a top-right corner of the CU (1453), andthe first sub-region (1464) is at a top-left corner of the CU (1454). Asillustrated in FIG. 14, a combined sub-region (1471) is located at acenter of the combined CU (1455), and crosses boundaries (1491)-(1494)of the neighboring CUs (1451)-(1454). Further, a width ratio and aheight ratio are 1/2. In one example, the multiple CUs (1451)-(1454) canbe coded with different motion prediction information. Operationssimilar to those described above can be implemented for the combinedsub-region (1471) and the combined CU (1455) at an encoder and a decoderside, respectively, and thus, a detailed description is omitted forpurposes of clarity. Further, in an embodiment, an additional flag, suchas a combined SVT flag, can be signaled to indicate that a CU, such asthe CU (1451), is a portion of the combined CU (1455) that includes themultiple CUs. A number of the multiple CUs, relative positions of themultiple CUs, a position, a size, and/or a shape of the respective firstsub-region within each of the multiple CUs, and/or the like can also besignaled.

FIG. 15 shows a flow chart outlining a process (1500) according to anembodiment of the disclosure. The process (1500) can be used in thereconstruction of one or more blocks coded with inter prediction. Invarious embodiments, the process (1500) can be executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230) and (240), the processing circuitry that performsfunctions of the video encoder (303), the processing circuitry thatperforms functions of the video decoder (310), the processing circuitrythat performs functions of the video decoder (410), the processingcircuitry that performs functions of the video encoder (503), theprocessing circuitry that performs functions of the predictor (535), theprocessing circuitry that performs functions of the decoder (710), theprocessing circuitry that performs functions of the inter decoder (780),the processing circuitry that performs functions of the reconstruction(774), and/or the like. In some embodiments, the process (1500) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1500).

The process (1500) starts at (S1501) and proceeds to (S1510). At(S1510), encoding information associated with a CU of a picture in acoded video bitstream is decoded. The CU can be a luma coding CU, achroma coding CU, or the like. The CU can have any suitable shape, size,and the like. The CU has a rectangular shape according to an embodiment,such as a square shape. In an example, the encoding informationindicates that the CU is coded using inter prediction, and includes aSVT flag. The encoding information can also include additionalinformation of a SVT pattern, such as a position, a shape, and/or a sizeof the SVT pattern with respect to the CU.

In some embodiments, the encoding information can also include acombined SVT flag to indicate that the CU is a portion of a combined CU,a number of multiple CUs in the combined CU, relative positions of themultiple CUs, a position, a size, and a shape of respective firstsub-regions within each of the multiple CUs, and/or the like.

At (S1520), whether a SVT is associated with the CU is determined basedon the encoding information. For example, when the encoding informationincludes the SVT flag, the CU is determined to be associated with theSVT. In another example, when the encoding information indicates thatthe CU is coded using intra prediction, the CU can be determinedimplicitly not to be associated with a SVT. Alternatively, when the CUis coded using inter prediction and a SVT flag is not signaled, the CUcan be determined implicitly not to be associated with a SVT. When theCU is determined to be associated with the SVT, the process (1500)proceeds to (S1530). Otherwise, the process (1500) proceeds to (S1525).

At (S1525), samples in the CU are reconstructed based on residual dataof the samples according to a suitable video coding technology and/or avideo coding standard, such as the HEVC standard, the VVC standard, andthe like. Subsequently, the process (1500) proceeds to (S1599), andterminates.

At (S1530), a SVT pattern including, for example, a position and a sizeof a first sub-region in the CU can be determined from the encodinginformation. As described above, the CU includes a first sub-regionhaving first samples and a second sub-region having second samples wherethe second samples are outside the first sub-region.

The first samples inside the first sub-region are reconstructed based onresidual data of the first samples. For example, an inverse transform isimplemented on transform coefficients associated with the first samplesto obtain the residual data of the first samples.

When the CU is determined to be a portion of the combined CU asdescribed in (S1520), a combined sub-region within the combined CU isdetermined based on the encoding information. First samples inside thecombined sub-region that includes the first sub-regions of therespective multiple CUs are reconstructed based on residual data of thefirst samples. In an example, a single inverse transform is implementedon transform coefficients associated with the first samples of thecombined sub-region to obtain the residual data of the first samples.The multiple CUs can be coded with different motion predictioninformation, and thus, the first samples from the multiple CUs can bereconstructed using the different motion prediction information,respectively.

At (S1540), the second samples inside the second sub-region (and outsidethe first sub-region) are reconstructed without residual data. Forexample, the second samples of the CU can have the same motionprediction information with that of the first samples, and arereconstructed using the same motion prediction information.

When the CU is determined to be a portion of the combined CU asdescribed in (S1520), the second samples of the combined CU that areoutside the combined sub-region are reconstructed without residual data.For example, the multiple CUs can be coded with different motionprediction information, and thus, the second samples from the multipleCUs can be reconstructed using the different motion predictioninformation, respectively. Subsequently, the process (1500) proceeds to(S1599), and terminates.

As described above, a CU can include one or more coding blocks (CBs),such as one luma CB and two chroma CBs, where a CB includes a 2D samplearray of a single color component associated with the CU. Therefore, theabove description can be applied to a CB or multiple CBs.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bidirectional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks and networkinterfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough a system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit-   QT: Quadtree-   AMVP: advanced motion vector prediction

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding encoding information for a block of a picture in acoded video bitstream, the encoding information indicating a position ofa sub-region in the block and a position of an additional sub-region ineach of at least one neighboring block of the block, a combinedsub-region including the sub-region and the additional sub-region ineach of the at least one neighboring block being at a center of acombined block including the block and the at least one neighboringblock; reconstructing first samples that are inside the combinedsub-region using residue data of the first samples; and reconstructingsecond samples that are outside of the combined sub-region in thecombined block without residue data.
 2. The method of claim 1, whereinthe combined sub-region and the combined block have a rectangular shape.3. The method of claim 2, wherein a number of the at least oneneighboring block is one and the at least one neighboring block islocated to one of: the right of the block and below the block.
 4. Themethod of claim 2, wherein a number of the at least one neighboringblock is three and the block is located at a top-left corner of thecombined block.
 5. The method of claim 2, wherein a width ratio of awidth of the combined sub-region over a width of the combined block is1/2, and a height ratio of a height of the combined sub-region over aheight of the combined block is 1/2.
 6. The method of claim 1, whereinthe block and the at least one neighboring block are coded using interprediction, and motion prediction information for the block is differentfrom motion prediction information for the at least one neighboringblock.
 7. The method of claim 1, wherein the block and the at least oneneighboring block are coded using inter prediction, motion predictioninformation for the block and the at least one neighboring block issignaled before information of the residue data of the first samples. 8.The method of claim 1, wherein the encoding information furtherindicates a size of the sub-region and a size of the additionalsub-region in each of the at least one neighboring block of the block.9. A method for video decoding in a decoder, comprising: decodingencoding information for a block of a picture in a coded videobitstream, the encoding information indicating a combination of aposition of a sub-region in the block and a relative size of thesub-region with respect to the block, wherein first samples inside thesub-region are reconstructed using residue data of the first samples,second samples of the block that are outside of the sub-region arereconstructed without residue data, and the combination of the positionand the relative size is one of multiple combinations of differentpositions and different relative sizes; reconstructing the first samplesof the block that are inside the sub-region using the residue data ofthe first samples; and reconstructing the second samples of the blockthat are outside of the sub-region without residue data.
 10. The methodof claim 9, wherein the block and the sub-region have a rectangularshape; the relative size is associated with a width ratio being a widthof the sub-region over a width of the block and a height ratio being aheight of the sub-region over a height of the block; and the multiplecombinations of different positions and different relative sizesinclude: 1) the position is a center of the block, the width ratio andthe height ratio are 1/2, 2) the position is a center of the block, thewidth ratio is 1/2 and the height ratio is 1, 3) the position is a leftside of the block, the width ratio is 1/4 and the height ratio is 1, 4)the position is a right side of the block, the width ratio is 1/4 andthe height ratio is 1, 5) the position is a center of the block, thewidth ratio is 1 and the height ratio is 1/2, 6) the position is a topside of the block, the width ratio is 1 and the height ratio is 1/4, and7) the position is a bottom side of the block, the width ratio is 1 andthe height ratio is 1/4.
 11. The method of claim 9, wherein: theencoding information includes an index indicating the one of themultiple combinations of different positions and different relativesizes; and the method further includes receiving the index in the codedvideo bitstream.
 12. The method of claim 9, wherein the differentrelative sizes include a relative size of the sub-region being 1/4 ofthe block.
 13. An apparatus, comprising processing circuitry configuredto: decode encoding information for a block of a picture in a codedvideo bitstream, the encoding information indicating a position of asub-region in the block and a position of an additional sub-region ineach of at least one neighboring block of the block, a combinedsub-region including the sub-region and the additional sub-region ineach of the at least one neighboring block being at a center of acombined block including the block and the at least one neighboringblock; reconstruct first samples that are inside the combined sub-regionusing residue data of the first samples; and reconstruct second samplesthat are outside of the combined sub-region in the combined blockwithout residue data.
 14. The apparatus of claim 13, wherein thecombined sub-region and the combined block have a rectangular shape. 15.The apparatus of claim 14, wherein a number of the at least oneneighboring block is one and the at least one neighboring block islocated to one of: the right of the block and below the block.
 16. Theapparatus of claim 14, wherein a number of the at least one neighboringblock is three and the block is located at a top-left corner of thecombined block.
 17. The apparatus of claim 14, wherein a width ratio ofa width of the combined sub-region over a width of the combined block is1/2, and a height ratio of a height of the combined sub-region over aheight of the combined block is 1/2.
 18. The apparatus of claim 13,wherein the block and the at least one neighboring block are coded usinginter prediction, and motion prediction information for the block isdifferent from motion prediction information for the at least oneneighboring block.
 19. The apparatus of claim 13, wherein the block andthe at least one neighboring block are coded using inter prediction,motion prediction information for the block and the at least oneneighboring block is signaled before information of the residue data ofthe first samples.
 20. The apparatus of claim 13, wherein the encodinginformation further indicates a size of the sub-region and a size of theadditional sub-region in each of the at least one neighboring block ofthe block.